Conventionally, an interference check is performed in a numerical control machine tool to prevent interference between a tool rest and a holding means for holding a workpiece. The holding means may be a jig such as chuck jaws or a vise. Typically, in an interference check for chuck jaws, a chuck barrier is defined on an X-Z plane for each chuck jaw, and it is determined whether the tool rest or the cutting edge of the cutter enters the chuck barriers, while the tool rest or a cutter of a tool is moved on the X-Z plane (see Patent Document 1). Parameters necessary for setting chuck barriers are set in advance before shipment of the numerical control machine tool. As a result, simply by setting the jaw shape, a user can perform an interference check.
In case of milling a workpiece, the cutting edge of a tool may have to enter a gap between two jaws. In this case, an interference check is canceled before executing a machining program. Specifically, the chuck barriers are canceled so as to allow the cutting edge of the tool to enter the gap between the jaws. This makes it necessary for the operator to perform a visual interference check throughout the processes of the machining program. As a result, the operator may erroneously allow an interference between the tool rest and the holding means to occur.
Patent Document 2 discloses a method for selectively activating and de-activating an interference check between a cutting tool and a non-safety zone. According to this method, it is determined whether a machining program to be carried out is a legitimate program written according to a legitimate procedure depending on whether there is specific code written in this machining program. If the machining program is a legitimate program, the movement of the cutting tool is prevented from automatically stopping even when the cutting tool enters the non-safety zone.
However, this method requires a prolonged time for editing programs in advance and checking for interference in an actual machine tool when in an initial product machining after completion of program writing.
Patent Document 3 is a publication representing the state of the art at the time of filing.